The skin is the largest organ of the body and acts as the first line of defense. It has several important functions, including protection, regulating body temperature, decreasing water loss, containing sensory receptors, synthesizing biochemicals, and excreting waste. The skin is composed of three main regions - the epidermis, dermis, and subcutaneous layer. The epidermis is the outermost layer and lacks blood vessels. It contains keratin-producing cells, melanin-producing cells, immune cells, and touch receptors. The dermis lies beneath the epidermis and contains strong connective tissue, blood vessels, nerves, hair follicles, and muscles. The deepest layer is the subcutaneous tissue,

2. General Facts:
A.First line of defense
B.Vital to homeostasis
C.Largest body organ

3. Functions of the skin:
1. Protection
2. Regulate body temperature
3. Decrease water loss
4. Contains sensory receptors
5. Synthesize biochemicals
6. Excrete waste

4. Regions
Epidermis –
outermost layer
Dermis – middle
layer
Subcutaneous–
deepest layer

5. Epidermis
• Composed of cells in four or five layers
• Lacks blood vessels
• Outer portion of the skin that is exposed to
the external environment and functions in
protection

7. Cells of the Epidermis
• Most cells in the epidermis produce the
fibrous protein keratin
• Some cells produce the brown pigment
melanin
• Some cells turn on the immune system
• Some cells function as touch receptors in
association with sensory nerve endings

8. Skin Color
Three pigments contribute to skin color
•Melanin – yellow to reddish-brown
to black pigment, responsible for
dark skin colors
•Carotene – yellow to orange pigment,
most obvious in the palms and soles
of the feet
•Hemoglobin – reddish pigment
responsible for the pinkish hue of the
skin
Sunlight causes the melanin production to increase.
Circulation with dermal blood vessels affects skin color.

9. Dermis
• Second major skin region
containing strong, flexible
connective tissue
(collagen fibers) and
blood vessels that carry
nutrients to upper layers
of skin and help regulate
body temperature

10. Also consists of
nerves, hair
follicles, sweat
glands, oil glands
and muscles.

11. Subcutaneous (Hypodermis)
• Deepest layer of the skin
• Composed of a fatty layer and loose
connective tissue
• It binds the skin to underlying organs and
contains the blood vessels that supply the
skin.
• There is no sharp boundary between the
dermis and the hypodermis